| The Electrolyte Nonrandom Two-Liquid Activity Coefficient model in Aspen Plus(TM) 2006.5 was used to develop a rigorous and consistent thermodynamic representation for the base sub-component systems associated with aqueous combinations of K2CO3, KHCO3, MEA, and piperazine (PZ) in a mixed-solvent electrolyte system for the application of CO 2 absorption/stripping from coal fired power plants.;We developed a new vapor-liquid equilibrium apparatus to measure CO 2, amine, and H2O vapor pressures at 40 and 60 °C. We found that the volatility of MEA and PZ can be approximated at 50 and 20 ppm v at 40 °C for any solvent composition studied in this work, over the CO2 partial pressure range from 0.01 to 0.1 kPa. Very few solvent compositions exhibited a greater differential capacity than 7 m MEA at 60 °C; specifically 11 m MEA, 3.5 m MEA + 3.6 m PZ, 7 m MEA + 2 m PZ, 7 m MEA + 3.6 m PZ, and 5 m K+ + 7 m MEA + 3.6 m PZ. Piperazine exhibited a possible maximum differential capacity of 2.21 mole CO2/kg-H 2O at a concentration of 7.3 m.;At the Norwegian University of Science and Technology, Inna Kim determined the differential enthalpy of CO2 absorption for aqueous combinations of K2CO3, KHCO3, MEA, PZ, and CO2, based on a consistent experimental method developed for MEA, from 40 to 120 °C for use in this work. In addition, we developed a consistent method to measure the specific heat capacity for a number of similar solvent combinations. We found that the enthalpy of CO2 absorption increased with temperature because the apparent partial heat capacity of CO2 may be considered small.;Finally, by using a differential scanning calorimeter, we determined the dissolution temperature for aqueous mixtures of unloaded piperazine, which inferred an effective operating range for solutions of concentrated piperazine, greater than 5 m PZ, over a loading range between 0.25 to 0.45 mole CO 2/2·mol PZ. Through unit cell x-ray diffraction, we were able to identify and characterize the presence of three solid phases (PZ·6H 2O, KHCO3, and K2PZ(COO)2) in aqueous mixture combinations of K2CO3, KHCO3, PZ, and CO2. |
